In the oil and gas industry, in order to grip drill pipe it is necessary to apply high gripping forces while simultaneously rotating the pipe or restraining the pipe against rotation. Typically, such forces are now applied to pipe through the use of power tongs or a back-up tong. Within a power tong, a jaw assembly is rotatably mounted with provision for jaw surfaces within the assembly to receive and embrace the pipe once torque is to be applied. A back-up tong has similar jaw surfaces.
It is normal to use gripping plates which are inserted into the jaw assembly as the actual component that contacts with the pipe. These jaw plates or die inserts are typically made of hardened metal, and/or carry a gripping, eg. textured, surface which is suited for developing a high; frictional contact with the surface of pipe. They may also have smooth surfaces formed on softer metal. Such die inserts are installed within a jaw assembly at the focal point for the forces which are to be applied to pipe. Those forces include a rotational torque intended to turn the pipe in order to make or break pipe joints or carry-out rotation for drilling; a compressional force caused by the camming surface of the rotary gear forcing the jaw assembly to press up against the pipe, and vertical forces arising, as for example, when the weight of a power tong rests upon, or is dropped onto, the pipe.
As such jaw plates are subject to wear, they must be readily replaceable within the jaw assembly. Various systems for attaching jaw plates within a jaw assembly have been proposed. In particular, U.S. Pat. Nos. 4,576,067; 5,911,796 and 6,253,643 all to Buck describe a removable die plate which is provided with an external, convex surface having splines which run vertically. These splines mate with complementary grooves formed in the body of the jaw assembly. The splines serve to provide the necessary torque transfer between the jaw assembly and the jaw plates, serving to hold the die plate in place while rotating forces are applied to the pipe.
In U.S. Pat. No. 4,576,067 the jaw plate or die is held vertically in place by conventional means such as a screw that engages with a lip protruding from the convex surface of the die plate. While the splines of this prior invention provides a much greater and more robust surface area between the jaw assembly and the die plate to transfer rotational forces, the screw and lip arrangement makes little provision to absorb vertical forces that may arise when a section of pipe is lowered or raised vertically, carrying the power tong with it. The vertical forces arising under oil field conditions may be substantial. In the referenced U.S. patent above the only provision to accommodate such forces is the screw and lip feature as described. Depending on the dimensions of these components the lip and screw feature may be inadequate to support substantial vertical loads.
In U.S. Pat. No. 6,253,643 upper and lower lips or ledges are provided to contain the jaw plate. These lips are removeably attached to the jaw assembly by fasteners. To more securely absorb vertical loads arising between the jaw plate and jaw assembly, a curved insert is fitted into a keyway provided by opposed annular slots formed in the jaw plate and jaw assembly splined surfaces. Thus installation of this jaw plate also requires manipulation of an insert.
In the case of prior art designs the splines are cut with gear-like orientations. Consequently, the jaw plate must normally be slid into place. The die plate in these disclosures may not readily fit directly in place by a face-on-face insertion procedure due to the angles of the outer splines and grooves along the die plate edges.
It is an object of this invention to provide an improved form of jaw plate or die that is adapted to better transfer vertical forces between the jaw plate and the jaw assembly to which it is mounted and is more easily fitted into place. It is a further object of this invention to provide improved means for restraining a jaw plate against vertically-applied forces.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims, which conclude this Specification.